Project Summary/Abstract The goal of the project is to develop a model that explains the processes by which decisions are made about information that is continuously distributed across one-dimensional and two-dimensional spaces, with responses made on continuous scales. Large comprehensive bodies of data will be collected in the domains of decision- making in perception, long-term memory, working memory, and numerosity and these will allow tight constraints on the theoretical assumptions of the modeling. The model will provide a unified explanation of the full range of data for continuous tasks, including accuracy, the distributions of response times for correct and incorrect responses, how they change with manipulations of independent variables, and how they differ among individuals and groups of individuals. Statistical properties of the model will be examined and the numbers of observations needed in experiments with clinical and other populations will be examined. The model and the data collected to test it will be completely new to decision-making research. Four populations of adults will be studied, young adults, unimpaired older adults, adults with Mild Cognitive Impairment (MCI), and adults with early Alzheimer's Disease (AD). The aim will be to understand how normal aging affects individual components of processing in continuous decision-making and how MCI and early AD affect the components. Almost no research has been conducted with AD and MCI patients modeling the time course of decision-making. It is not known if the components of decision-making are the same as those for adults who are not cognitively impaired or how independent variables affect their accuracy and RTs or whether a modeling approach can uncover preserved skills not discernible from accuracy and RT data alone. 1